The present invention relates, in general, to the field of circulating fluidized bed (CFB) boilers and, in particular, to improved impact type particle separator constructions comprised of individual impact type particle separator elements.
CFB boiler systems are known and used in the production of steam for industrial processes and/or electric power generation. See, for example, U.S. Pat. Nos. 5,799,593, 4,992,085, and 4,891,052 to Belin et al.; U.S. Pat. No. 5,809,940 to James et al.; U.S. Pat. Nos. 5,378,253 and 5,435,820 to Daum et al.; and U.S. Pat. No. 5,343,830 to Alexander et al. In CFB reactors, reacting and non-reacting solids are entrained within the reactor enclosure by the upward gas flow which carries solids to the exit at the upper portion of the reactor where the solids are separated by impact type particle separators. The impact type particle separators are placed in staggered arrays to present a path which may be navigated by the gas stream, but not the entrained particles. The collected solids are returned to the bottom of the reactor. One CFB boiler arrangement uses a plurality of impact type particle separators (or concave impingement members or U-beams) at the furnace exit to separate particles from the flue gas. While these separators can have a variety of configurations, they are commonly referred to as U-beams because they most often have a U-shaped configuration in cross-section.
When applied to a CFB boiler, a plurality of such impact type particle separators are supported within the furnace enclosure and extend vertically in at least two rows across the furnace exit opening, with collected particles falling unobstructed and unchanneled underneath the collecting members along the rear enclosure wall. The gap between each adjacent pair of U-beams in one row is aligned with a U-beam in a preceding or following row of U-beams to present a tortuous path for the flue gas/solids to navigate. The U-beams in each row collect and remove particles from the flow of flue gas/solids, while the flue gas stream continues to flow around and through the U-beam array.
These types of collection elements are generally relatively long in comparison to their width and depth. The shape of the collection elements is usually dictated by two considerations: namely, the collection efficiency of the U-beams themselves and the ability of the U-beams to be self-supporting. When these elements are used, they are generally placed at the furnace exit and not cooled. Their placement at the furnace outlet is to protect the downstream heating surfaces from erosion by solid particles. Thus, the U-beams are exposed to the high temperatures of the flowing stream of flue gas/solids, and the materials used for the U-beams must be sufficiently temperature resistant to provide adequate support and resistance to damage.
Long, self-supporting stainless steel plate channels have been successfully used in CFB boilers for the primary solids collector, but the “creep” strength of the commercially available and suitable alloys limits the length of the collection elements.
By breaking up the long collection channel into short segments, the required strength of each short segment is much less than for the long channel due to the series of intermittent supports and the small amount of weight of any individual segment or element.
Collection elements which are cooled or supported off a cooled structure are known. See, for example, U.S. Pat. Nos. 6,322,603 B1 to Walker, U.S. Pat. No. 6,500,221 B1 to Walker et al., and U.S. Pat. No. 6,454,824 B1 to Maryamchik et al., the texts of which are hereby incorporated by reference as though fully set forth herein. These collection elements are well-suited to the environment and task of separating solids particles from flue gas, and are easier to maintain or repair than conventional U-beams comprised of self-supporting stainless steel plate channels.